Aluminum base alloy powder product



ALUMINUIVI BASE ALLOY POWDER PRODUCT Raymond J. Towner and John P. Lyle,In, New Kensington, Pa., assignors to Aluminum Company of America,Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Filed Mar.27, 1 958, Ser. No. 724,232

'3 Claims. (Cl. 29-182) This invention relates to articles made fromaluminum base alloy powders, and its is more particularly concerned withthose products resulting from heating and working a compacted mass ofatomized particles of an aluminum-zirconium base alloy.

Heretofore, compressed and sintered bodies of oxidecoated aluminum flakepowders have been produced which possess unique strength properties atelevated temperatures. The particles of oxide distributed throughout thebody appear to impart the unusual strength at elevated temperatures. Theproduction of the oxide coated flakes is time consuming and consequentlyexpensive. It has now been found, contrary to previous belief, thatuseful articles can be made from certain types of atomized aluminumalloy powders. As is well known, the automization process involvesdisintegrating a stream of molten metal with a jet of gas, such ascompressed air, or by mechanical means. Very finely divided particlescan be produced by this process which pass through a standard Tyler 100mesh screen.

It is an object of this invention to provide articles having a highstrength at elevated temperatures which are made from atomized particlesof an aluminum base alloy containing zirconium as the principal addedalloy component.

Another object is to provide such articles which do not require anypreliminary thermal treatment to place them in condition for service atelevated temperatures.

Still another object is to provide an article made from atomizedaluminum-zirconium alloy powder that does not depend upon the presenceof oxide particles to impart strength at elevated temperatures.

These and other objects are achieved by atomizing a substantiallyiron-free aluminum base alloy containing not less than 70 percent byweight of aluminum and from 3.5 to 15% by weight of zirconium as theprincipal added alloy component and subsequently consolidating andworking a mass of such atomized particles under the influence of heatand pressure. The resultant articles have a density closelyapproximating that of the alloy if cast; and in the worked conditionthey have a tensile strength of not less than 10,000 psi and a minimumyield strength of 9,000 psi. at 600 F. after a 100-hour exposure. Thesetensile and yield strength values are to be compared with those of someconventional Wrought heat treated aluminum base alloys that have beenrecommended for service at elevated temperatures. For example, a wroughtaluminum base alloy nominally composed of aluminum, 12.2% silicon, 1.1%magnesium, 0.9% nickel and 0.9% copper in the solution heat-treated andage-hardened condition has a tensile strength of only 5,000 p.s.i. and ayield strength of 3,000 psi. after an exposure of 100 hours at 600 F.Under the same exposure conditions, a second well-known aluminum basealloy nominally consisting of aluminum, 4.5% copper, 1.5% magnesium and0.6% manganese, when worked, solution heat treated and age hardened, hasa tensile 2,966,736 rammed Jalll. 3, 1951 ice strength of 10,000 p.s.i.and a yield strength of 7,500 psi. The aluminum-zirconium powderproducts can be readily worked under the usual hot working conditions oftemperature and pressure employed in fabricating conventional aluminumand aluminum base alloy articles. Furthermore, the hot-worked productcan be cold worked to a limited extent, if desired. The fabricated alloyproduct can be placed in service without any preliminary thermaltreatment. The strength of the wrought powder products at elevatedtemperatures is not influenced to any significant extent by the oxidefilm which coats the atomized particles.

The atomized alloy particles are preferably prepared by melting thealloy in the desired composition and projecting'it through a suitablydesigned nozzle with the aid of a compressed gas. The atomizingcondition should be so adjusted that none or only a small proportion'ofthe particles are larger than mesh microns opening) and that themajority of the particles pass through a 200 mesh screen (74 micronsopening). Articles produced in this manner generally have an irregularshape but for the most part are substantially equiaxed in dimensions andhave an as-cast structure. The aluminum-zirconium constituent in thealloy is very finely divided as the result of the drastic chillassociated with the atomization process. The surface of the particlesare, of course, oxidized if the atomization has occurred in air orinsome other oxidizing atmosphere, however, the oxide skin is very thinand the amount of oxide iritroduced ino the final product is too smallto affect the properties thereof to any significant extent.

The zirconium content of the alloy should be between 3.5 and 15 byweight, as mentioned above, and prefer.- ably within the range of 5 to10% to obtain the highest strength at elevated temperatures. If lessthan 3.5% is employed, the minimum strength is not achieved; and if morethan 15% is present, the worked article has insuificient ductllity andmay fracture under applied stresses. Zirconium is substantiallyinsoluble in aluminum and whatever small proportion may be dissolved istoo small to have any significant effect upon the properties of theatomized particles. It will, therefore, be appreciated that the matrixof the atomized particles consists of aluminum with a dispersion offinely divided aluminum-zirconium constituent distributed throughout theparticle. The high strength at elevated temperatures appears to becontrolled by the amount of the aluminum-zirconium constituent and thefineness of the dispersion.

The alloy may contain the usual impurities associated with aluminum, forexample, silicon and iron. Generally, the silicon impurities should notexceed 1% and the iron content should not be more than about 1%. Otherimpurities, such as copper, may also be present in amount up to 1%. Inview of the relatively small amount of iron impurity permitted in thealloy, the com position is referred to herein as being substantiallyironfree.

For some purposes, it may be desirable to add one or more of theelements selected from the group composed of manganese, nickel, cobalt,chromium, vanadium, titanium, molybdenum and tungsten in amount of 0.1to 10% by weight of each, the total not exceeding 10%. These elementsact as hardeners and, like zirconium are substantially insoluble in thealuminum matrix. To obtain the properties attributable to thealuminum-zirconium constituents, the zirconium content in the alloyshould exceed the total amount of any added hardener elements.

To make the wrought article from atomized powder, the powder may beinitially formed into a compact that is subsequently worked or it may becharged directly to a compression chamber, such as an extrusion presscylinder, and be extruded therefrom after initial consolidation of themass. The initial compact may be made by heating the powder to atemperature between 700 and 900 F. and applying a sufiicient pressurethereto for a long enough period of time to cause at least some Tensilespecimens were cut from the extruded rod and tested without anypreliminary thermal treatment, some at room temperature and others at600 F. after a 100- hour exposure at that temperature. The compositionof the alloys and the tensile strength at both room temperature and 600F. are given in Table I below:

consolidation on the welding of the atomized particles. Pressures of 200to 150,000 p.s.i. are satisfactory which are applied for varying periodsof time from a minute or less to a few hours. Generally, a longer timeis required where low pressures are employed. The compact may be left inthe press cylinder and then extruded, or it may .be ejected, cooled,scalped, reheated to the hot working temperature and hot worked. In somecases it may be desirable to reheat the compact to temperatures as highas 1150 F. for hot working or to obtain adequate workability.

Where the powder is charged to a compression chamber, it may beinitially heated to a temperature between 700 and 900 F. and introducedto the chamber or it may be charged cold and heated within the chamber.Alternatively, it may be heated to an intermediate temperature andbrought to the desired temperature in the compression chamber. Where thepowder is charged to a press cylinder, compacted and immediatelyextruded, it is generally convenient to compress the powder mass againsta blind die and then substitute a die with the desired orifice therein.Although reference has been made to the extrusion of the powder mass, itis to be understood that it can be subjected to other types of hotworking operations, such as rolling, forging or pressing, proyiding asuitable compact is initially produced. The hot working is preferablyperformed within the temperature range of 700 to 900 F.

Our invention is illustrated by the following examples whereinaluminum-zirconium atomized powders were consolidated and the producthot worked. The powders were of a fineness such that approximately 70%.passed through a 200 mesh screen and substantially all of the remainderpassed through a 100 mesh screen. Each powder was charged to anextrusion press cylinder, preheated to 800 F. and compressed against theblind die under a pressure of 100,000 p.s.i. for a period ofapproximately one minute. In the course of charging and compressing thepowder, the temperature of the compact reached 700 to 800 F. After thecompact was thus formed, it was ejected from the cylinder, cooled,scalped, and reheated for hot working. These compacts were reheated to850 F., inserted in an extrusion press cylinder heated to 800 F. andextruded to diameter rod.

It is apparent from the foregoing that the tensile and yield strengthsof the alloys increase with an increase in the zirconium content. Thetensile properties obtained at 600 F. are considerably higher than thoseof the two commercial aluminum base alloys referred to hereinabove. Itis also significant that the high strengths at 603 F. were obtainedwithout any preliminary thermal treatment of the worked powder product,such as solution heat treatment, which is a definite economic advantage.

Having thus described our invention and certain embodiments thereof, weclaim:

1. A hot worked aluminum base alloy powder article free from aluminumoxide except as incidental impurity and having a maximum iron content of1%, said hot worked alloy powder article being formed from atomizedpowder of alminum base alloy containing at least by weight of aluminumand from 3.5 to 15% by weight of zirconium as the essential component,the amount of said component exceeding the total of any hardeningelements present in the alloy, said alloy being substantially free fromelements which form a solid solution with aluminum, except as they occuras impurities, said hot worked article being characterized in theas-worked condition by tensile strength at 600 F. after a hour exposureof not less than 10,000 p.s.i. and yield strength not less than 9,000p.s.i.

2. A hot worked aluminum base alloy powder article according to claim 1wherein the zirconium content is 5 to 10% by weight.

3. A hot worked aluminum base alloy powder article according to claim 1wherein the alloy also contains at least one hardening element selectedfrom the group consisting of manganese, nickel, cobalt, chromium,vanadium, titanium, molybdenum and tungsten in amounts of 0.1 to 10%each, the total not exceeding 10% by weight, the zirconium content ofsaid alloy exceeding the total amount of hardening elements addedthereto.

References'Cited in the tile of this patent UNITED STATES PATENTS Noticeof Adverse Decision In Interference N o. 92 and J. P. Lyle, Jr.,Alumlnum base all oy powder product, final decision adverse to thepatentees was rendered Jul y 9, 1963, as to claims 1 and 2. [OfiiemlGazette September 3, 1963.]

in Interference ,634 involving Patent No. 2,966,736, R. J. Towner

1. A HOT WORKED ALUMINUM BASE ALLOY POWDER ARTICLE FREE FROM ALUMINUMOXIDE EXCEPT AS INCIDENTAL IMPURITY AND HAVING A MAXIMUM IRON CONTENT OF1%, SAID HOT WORKED ALLOY POWDER ARTICLE BEING FORMED FROM ATOMIZEDPOWDER OF ALUMINUM BASE ALLOY CONTAINING AT LEAST 70% BY WEIGHT OFALUMINUM AND FROM 3.5 TO 15% BY WEIGHT OF ZIRCONIUM AS THE ESSENTIALCOMPONENT, THE AMOUNT OF SAID COMPONENT EXCEEDING THE TOTAL OF ANYHARDENING ELEMENTS PRESENT IN THE ALLOY, SAID ALLOY BEING SUBSTANTIALLYFREE FROM ELEMENTS WHICH FORM A SOLID SOLUTION WITH ALUMINUM, EXCEPT ASTHEY OCCUR AS IMPURITIES, SAID HOT WORKED ARTICLE BEING CHARACTERIZED INTHE AS-WORKED CONDITION BY TENSILE STRENGTH AT 600*F. AFTER A 100 HOUREXPOSURE OF NOT LESS THAN 10,000 P.S.I. AND YIELD STRENGTH NOT LESS THAN9,000 P.S.I.